In their 20 years as partners, architects Joe Tanney and Robert Luntz have designed dozens of sleekly modern houses (plus dozens more lofts and apartments). Among the trademarks of their firm, which is called Resolution: 4 Architecture, are interior walls of hot rolled steel. In this upstate New York weekender, one such wall anchors a corner of the living room, where the architects knew it would pop against the floor-to-ceiling glass and the maple floorboards.

But even Tanney and Luntz didn't know how good the wall would look until the owners, Charles and Xiomara Scheidt, brought in Amy Lau as their interior designer. To enliven it, she chose an inexpensive abstract painting that she purchased on an auction website. Like the room around it, the painting is autumnal: Lau first visited the house on a bright fall day and was inspired by the orange, red and yellow leaves visible everywhere. And, like the room around it, the painting is dynamic, suggesting motion in the same way Lau's furniture arrangement energizes the simple glass-enclosed space.

A founder of Design Miami, Lau has an encyclopedic knowledge of 20th-century decorative arts. In implementing her plan for the Scheidts' house, Lau says, she was as much a curator as a decorator, including pieces by both well-known designers (the sectional sofa is by Edward Wormley for Dunbar) and lesser-known greats like Denmark's Greta Jalk, who designed the swoopy chair and ottoman. Thanks to the architecture—which is restrained, modern and at the same time lively—the furniture feels right at home.

Homeowners Charles and Xiomara Scheidt were looking for a getaway not far from New York City, but they didn't have exactly the same getaway in mind. As Tanney recalls: "He wanted a vernacular Adirondacks cabin, but she wanted a modern Manhattan loft." So the architects gave them a little of each. Says Tanney: "The stone and wood are for Charles; the glass and steel for Xiomara."

The house was already under construction when the Scheidts brought in Amy Lau. "I tried to have a dialogue with the architecture," says Lau. In the dining area, where the architects provided a simple maple wall, Lau responded in kind, choosing a Jens Risom table that makes the most of a single slab of rosewood (a table with leaves, she explains, wouldn't have the same power).

Over the table is a chandelier that suggests fall foliage. Lau found it at an antiques fair. Once the fixture was installed, she learned that breezes through the house cause it to rustle gently. The house picks up the energy of the landscape, with the light fixture being the most literal example.

Even in the kitchen, where functional requirements could have intruded on the design, the architects relied on their years of experience to achieve the cleanest possible lines. For instance, they placed air vents in the toe kicks beneath the counters, rather than on walls or ceilings, which is both more usual and more visually intrusive. The Resolution: 4 architects also avoided upper cabinets in order to maximize window space. Shelves hanging from tie rods seem to float above the lake. Lau did her part by arranging small, translucent objects that dazzle the eye but don't stop it from taking in the view.

"We fell in love with the site," says Xiomara, explaining how she and her husband acquired a 1940s bungalow an hour north of New York City. But the building, which was falling apart, was no match, aesthetically, for the waterfront property. "We'd go out to the lake and we'd come back and be all depressed," she says. Friends recommended architects Luntz and Tanney, who have made a specialty of creating modern houses that are smartly detailed and yet surprisingly affordable to build. Their firm has designed dozens of prefabricated houses, valuable experience for creating sleek details that can be reproduced at modest cost. In this case, they retained the original foundation to avoid unnecessary expenditures.

Above the foundation they created a 2,400-square-foot house with large and small windows carefully located in relation to the sun's movement. Take the tiny window in the corner of the guest room (above). The architects positioned it "to allow views up into the trees, but not out onto the private guest deck," says Tanney. "More important," he adds, "it faces south and allows a controlled beam of light to trace a path across the interior. At midday, the sun hits the back wall, reflecting light into the room."

Not surprisingly, Lau was determined not to upstage the carefully thought-out architecture with the interior design. That's why she painted the bedroom white rather than the vibrant colors she often specifies. And the items she chose for the room, including a Swedish rya rug, a hand-embroidered throw by Judy Ross and a wooden ball lamp by Muriel Coleman, are intriguing without being overpowering. Says Lau of the architects, "We didn't work together, but it's seamless."

What The Pros Know

The master bathroom contains a barely there shower "stall" consisting of a single piece of glass to contain the spray. The architects had a sheet of ⅜-inch tempered glass cut two inches longer than the room is tall. That enabled them to insert the top and bottom of the glass into recessed aluminum channels. When the ceiling and floor were finished, the metal channels disappeared. The floors and walls are covered in six-inch slate tiles, which are tricky to install on a floor that has to slope toward a drain from two directions. (If you're not sure your contractor will get the slope just right, Luntz recommends using one-inch "mosaic" tiles, which are easier to manipulate on angles than the larger slabs.) The architects' most important tip: If you aren't having curbs around the shower area, you have to keep the water draining quickly. For that, use a three-inch, rather than the usual two-inch, drain, or even a pair of three-inch drains, says Luntz, who adds: "You can never have too much drain."